Conventionally, some ball-point pens especially designed for fine writing are provided in which their writing tips are reduced in diameter. There is a purpose of reducing an area as much as possible in which the writing tip may hide written lines in the case of writing and drawing small and fine letters and figures. The thus diameter-reduced writing tips are accepted in the market, which are made from a pipe-like material by way of plasticity processing or cutting, or formed from a cylindrical material by cutting, for example.
As described above, when the writing tip is reduced in diameter, a problem arises in that its tip end to which writing pressure is applied has poor rigidity, and that as the tip is reduced in diameter, its inner diameter i.e., an ink passage is also reduced in diameter so that an insufficient amount of ink is supplied to the writing ball side at the top end. Thus, there arises a technical condition that axial length of the writing tip must be designed to be as short as possible. Therefore, a joint member into which the writing tip is press-fitted and which is made of a less glittering synthetic resin is extended to the vicinity of the top end of the writing tip, leading to a secondary problem of damaging its appearance.
Each of the following patent documents discloses a ball-point pen structure for compensating for the insufficient rigidity of the writing tip end to which the above-mentioned writing pressure is applied and for preventing the writing tip from being bent and swinging. In other words, Japanese Utility Model Publication (KOKAI) No. H7-37681 discloses a structure in which a metal cover member is employed to compensate for the poor rigidity of the writing tip. Japanese Patent Publication (KOKAI) No. H8-118876 discloses a structure in which a part of a metal cover member for compensating for lack of rigidity of a writing tip is further supported in abutment with a writing tip. Further, Japanese Patent Publication (KOKAI) No. H8-118877 discloses a structure in which a metal cover member for compensating for lack of rigidity of a writing tip is press-fitted to a perimeter of the writing tip.
FIGS. 12 and 13 show a structure of a metal cover member adopted for a ball-point pen as disclosed in the above-mentioned Japanese Utility Model Publication (KOKAI) No. H7-37681. In addition, FIG. 12 shows, in section, a situation where the cover member is about to be fitted onto a joint member along its perimeter surface. FIG. 13 shows, in section, a situation where the cover member is mounted on the perimeter surface of the joint member. In these FIGS. 12 and 13, reference numeral 1 indicates a writing tip at the top end of which a writing ball 2 is rotatably supported, reference numeral 3 shows a first joint member made of a synthetic resin onto which the above-mentioned writing tip 1 is press-fitted, and reference numeral 4 shows a second joint member similarly made of a synthetic resin into which the above-mentioned first joint member 3 is press-fitted further.
In addition, although not shown in these FIGS. 12 and 13, the above-mentioned second joint member 4 is further press-fitted into an ink storage tube as will be described later, to constitute a ball-point pen refill. It is arranged that ink passages 1a, 3a and 4a are respectively formed at the above-mentioned writing tip 1, first joint member 3, and second joint member 4 such that ink from the above-mentioned ink storage tube may be supplied toward the writing ball 2 disposed at the top end of the writing tip 1.
Further, a valve room 4b is formed in the above-mentioned second joint member 4 so as to be formed conical toward the ink passage 4a, and a ball valve 5 is accommodated in the valve room 4b. With this structure, for example, when writing upwards, the ball valve 5 achieves valve closing operation at the above-mentioned conical section of the valve room 4b, prevents the ink from flowing backwards, and acts to be able to prevent air from flowing into the writing tip 1.
It is arranged that a metal cylindrical cover member 6 may be mounted by fitting it on the first joint member 3 in the ball-point pen refill having the structure as described above along the perimeter surface of this joint member 3. As shown, this cover member 6 is constituted by a large diameter portion 6a and a small diameter portion 6b which are integral with each other. It is arranged that the large diameter portion 6a is fitted along the perimeter surface of the joint member 3 so that the small diameter portion 6b can surround first joint member 3 side of the writing tip 1.
Thus, according to the situation as shown in FIG. 13 where the cover member 6 is mounted and fitted along the perimeter surface of the joint member 3, the perimeter surface of the writing tip 1 is surrounded by the small diameter portion 6b of the cover member 6. Therefore, when the writing tip 1 is subjected to writing pressure to be about to bend and swing, the small diameter portion 6b of the cover member 6 is brought into contact with the writing tip 1 and acts to prevent this operation.
Patent document 1: Japanese Utility Model Publication (KOKAI) No. H7-37681
Patent document 2: Japanese Patent Publication (KOKAI) No. H8-118876
Patent document 3: Japanese Patent Publication (KOKAI) No. H8-118877